The communication field requires high frequency products for portable applications in the RF and microwave frequency ranges. The integrated circuits that help meet these needs generally require passive components such as capacitors and inductors for tuning, LC tanks, AC coupling, impedance matching, and filtering requirements. However, with regard to inductors, integrating inductors on the same substrate with active and/or passive components has been problematic. Conventional integrated inductors typically present high series resistance and substrate parasitic resulting in poor quality inductors (inductors with low Q, i.e., Q&lt;10). Consequently, passive components, including inductors, have typically been configured external to the integrated circuits containing the active components. Yet, external inductors present their own problems, including: requiring greater area/board space, introducing parasites associated with interfaces between integrated circuits and external components, lowering reliability due to more components and connections, and increasing cost due to higher component count and more complex assembly.
Where inductors have been integrated, the integrating has been accomplished using aluminum and gold metallization schemes with films typically less than 3 .mu.m thick. These inductors suffer from high series resistance due to their thin structure, and the relatively high resistivity of aluminum and gold. In addition, integrated inductors used in the past have been implemented such that they do not lie over other components of the overall circuit, which are in lower layers of the device substrate. There are several reasons why, in the past inductors have not been incorporated over other components of the circuit. These reasons include increased substrate parasitics due to the typically thin dielectric layer between the integrated inductor and underlying electronic devices. Additionally, air bridges which are typically used to construct inductors (common in some GaAs technologies to support the inductor metal), do not permit the construction of devices Under the air bridge. Furthermore, integrated inductors have required etching material under the inductor to lower capacitive coupling. Such etching below the inductor does not permit the construction of devices Under the inductor.
Since inductors in the. past have not been incorporated over other electronic circuitry, separate area for the integrated inductors has been required. Separate area for the inductors increases the space required on the integrated circuit and thus the cost of the circuit. Depending on the integrated circuit technology, this additional area may make the integrated inductor cost prohibitive.
Consequently, a need exists for a method of constructing a high quality inductor on the same substrate as other active and/or passive components.